1. Field of the Invention
This invention relates to an inverter apparatus for use in battery powered vehicle drives. More particularly, the invention relates to such an inverter apparatus which is selectively operable either to convert DC from a storage battery located on board the vehicle to supply a polyphase AC electric motor or alternatively to charge the battery from an external energy supply source.
2. Description of the Prior Art
The development of battery-powered vehicles for widespread use has presented a number of substantial technical challenges. Much of the effort to overcome these challenges has been concerned with increasing efficiency. This has made weight reduction a primary consideration. Also, the vehicle must be able to operate over a wide range of speed and torque requirements.
Some drive systems for battery-powered vehicles incorporate polyphase AC electric motors as the electro-mechanical energy converters. These drives are known to have relatively high efficiency as well as excellent control characteristics. When such motors are utilized, however, the battery voltage must be converted from DC to polyphase AC. Furthermore, in order for the motor to respond to instantaneous speed and torque requirements, the AC must be variable voltage and frequency. The mechanism for performing this conversion is typically a pulse-width modulated ("PWM") inverter. Such inverters are well known throughout the power electronics community.
No matter how efficient an electric vehicle is made, the storage batteries must inevitably be recharged. This has often required special external equipment. Thus, in order to increase the feasibility of these vehicles, it is desirable that the circuitry necessary to recharge the batteries be carried "on board." This allows the vehicle to be recharged from convenient external energy sources. Typical charging systems added to a vehicle, however, simply increase overall weight. Thus, improvement in convenience has been at the expense of weight which causes an increase in acceleration times and a reduction of vehicle range.